The invention concerns a filter device, in particular liquid filter, comprising an annular filter element and a functional part insertable into the filter element and extending parallel to the longitudinal axis of the filter element.
U.S. Pat. No. 3,749,247 discloses a filter device for oil filtration that comprises a folded annularly configured filter element which is flowed through by the oil to be purified in radial direction. In order to reduce the risk of oxidation of the oil, the filter device is provided with two cylindrical additive containers in which an additive inhibiting oxidation is contained that mixes with the oil upon flow through the filter device. The additive containers are arranged diametrically opposed parallel to the longitudinal axis of the filter element and integrated into the paper folds of the filter element. In case of radial inflow at the filter element from the exterior to the interior, the additive containers constitute an obstacle for the oil that accordingly must find a path through neighboring sections of the filter element.